Marking pen



FIG. 1 is a top plan view of a marking pen showing my new design;

FIG. 2 is a right side elevational view thereof, the left side view being a mirror image thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a right side elevational view thereof in open condition, the left side view being a mirror image thereof;

FIG. 5 is a front elevational view thereof in open condition. 

The ornamental design for a marking pen, as shown and described. 